I want to help with editor. I'm thinking about this task but can switch to something different. How can I help? Where can I find info/doc about LAND record type? Could somebody please break down this task for me?

From what I understand, the LAND data can't be properly represented/edited in a table, so there is not much to do here. The only functionality we might need from the table is to delete, clone or revert to default state. Right Zini?

You added a land record with an invalid name. That needs to be handled in the LAND table creator bar. The only valid IDs are of the format #x y
Instead of entering an ID string it might be better to have two integer fields for input.

Anyway, the LAND code wasn't written for that. I guess you may have trashed the data structure. In fact the esm/omwgame file format can not store LAND records with such an ID. No idea what kind of junk ended up being written to the file.